Polyamide resin has an excellent chemical resistance to organic solvents such as gasoline and to alkali liquids and also has a high fluidity and excellent heat resistance and creep resistance whereby it has been used as exterior materials and inner parts for engine room of automobiles. It is also compounded with carbon black or the like to bestow electric conductivity to suppress generation of static electricity and electrification and is bestowed with a function where discharge within a relatively short time is possible whereby it is used as a part for refueling system of automobile parts such as a cap for fuel tank.
However, polyamide resin has a disadvantage that changes in its size become big by absorption of water and a problem that impact strength significantly lowers by addition of carbon black or the like. It has been well known to compound the polyamide resin with carbon black for bestowing electric conductivity on polyamide resin but, when compounding amount of carbon black is increased for enhancing the electric conductivity, fluidity and physical properties of the composition are greatly deteriorated. Therefore, there has been a proposal where, in order to improve fluidity and molding property, polyamide resin is compounded with carbon black bestowing electric conductivity thereon and with a modified ethylene copolymer which suppresses dimensional change by absorption of water to enhance the impact resistance (Japanese Patent Laid-Open No. 58/093,756).
In those methods however, although fluidity and molding property are improved, improvement of impact resistance of the polyamide resin composition is insufficient. Since the impact resistance is low, it is likely that the modified ethylene copolymer dispersed in the polyamide resin composition is dispersed in a relatively big particle diameter. Accordingly, electric conductivity and impact strength which are the properties demanded for fuel tank caps are not compatible. In addition, since a modified soft ethylene copolymer is dispersed in a polyamide resin composition in a big dispersed particle diameter, although polyamide resin inherently has an excellent slidability characteristic, its sliding characteristic is significantly deteriorated in the resin composition of a polyamide type as such.
As a method in which those electric conductivity and impact resistance are made compatible, there has been a proposal for a method where a carbon black dispersing agent is compounded (Japanese Patent Laid-Open No. 11/180,171). However, that is insufficient in view of fluidity and suppression of dimensional change upon absorption of water and, moreover, there is a problem that the carbon black dispersing agent soils the metal mold upon a molding processing.